Recipe originally found here, with slight modifications.
Simmer a finely diced onion in 1 and 3/4 cup chicken broth until onion is soft
in separate skillet, mix 1/3cup flour and 1/4 cup butter (aka 1/2 stick), and salt and pepper to taste.
Mix together stirring constantly until looks incorporated and add to broth
Add 2 cups milk. whisk well.
About 1/2 cup swiss cheese and 1/2 cup chedder cheese
About 3 cups steamed broccoli (I used about 4 and 1/2 cups).
Add a little more salt and pepper.
A big pot of warm for the coldest night of the year
(which was last night at our house)